Process of carrying through gas reactions



Oct. 22, 1935. N, CARO ET AL 2,018,249

PROCESS OF CARRYING THROUGH GAS REACTIONS Filed July 5, 1929 2 Sheets-Sheet l FI' 7, PeE/EHTED y Z n ven fons' /V/MOOEM C3920 01.65.67 E. Fea/wc @UML/2" WENDLA/Vor vwo/W75 FVscf/Ee,

By MMM@ H Trae/VE YS Oct. 22, 1935. N. CARO Er AL4 PROCESS OF CARRYING THROUGH GAS REACTIONS 2 Sheets-Sheet 2 Filed July 5, 1929 coMusT/O/Y 6055s M u D mw E 2 m w .y m rw Mm L 0 @an R 1V w N a m n mw N 1v om l E T 22u zu 1 z a au 5 L 0T m ,MW 0 m. h

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I Geseke/6| TOWEE I I /T l l I l l I fs/DUAL L m ,nu m M s so E DE e M CM 9 M m 3. T i e M i l o G l l l l l l ll w Il wm L l| m 1|l/1 IIII E m e 8 .C www'. 3 H mAfm wm O mm QI TE 7,20 X /DE Patented Oct. 22, 1935 UNITED STATES PATENT OFFIQE PROCESS F CARRYING THROUGH GAS REACTIONS Application July 5, 1929, Serial No. 376,267 In Germany November 24, 1927 13 Claims.

The present invention relates to reactions between gases and particularly to those reactions involving the utilization of a catalyst which must be ConlOlled so as to take place within narrow pressure and temperature limits and also to the recovery of the reaction products from the reaction gases.

In carrying out catalytic gas reactions, in which the reaction must be controlled within narrow temperature and pressure limits, conventional methods cannot be employed to control the temperature and pressure.

It has been found, particularly in the case of highly exotnermic reactions which are sensitive to temperature, that the heat of the reaction may be regulated by diluting the reaction gases with an inert gas or gases. However, when it is desired to recover the valuable reaction products from the nal reaction mixture, the presence of large quantities of such inert gas or gases render such recovery difficult and cause an overload of, or necessitate the utilization of absorbers, towers, condensers, and so forth, employed in the recovery process.

Among the objects of the present invention are to provide a method of carrying out gas reactions in which gases may be added to the reaction mixture in such a way as to enable satisfactory control of the temperature and pressure in the catalytic zone, Without particularly rendering the recovery of the valuable reaction products from the final reaction mixture more difficult, and without greatly or undesirably increasing the load on the absorbers, towers, condensers, and the like, or necessitating the utilization of excessive capacity in such recovery apparatus.

In one embodiment of the present invention such additions are made to the reaction mixture for controlling the temperature, pressure, and so forth, as will per se be readily removed, or as will be converted into products which may be easily separated, from the desired reaction products, preferably before the recovery of such reaction products or which in themselves may give rise to valuable products in the catalytic zone, which last mentioned products may be recovered together with or separately from the primary reaction products desired.

For example, steam or carbon dioxide may be added to the incoming reaction gases, both of these gases being easily condensed, absorbed, or otherwise separated from the reaction gases, as in the form of an aqueous solution, after they have passed through the reaction zone. Instead oi using steam or carbon dioxide per se, hydrogen and carbon monoxide may be utilized in oxidation reactions with resultant formation of Water vapor or carbon dioxide, the additional advantage being had in such case that the combustion of the hydrogen or carbon moni oxide in the catalytic zone will generate heat and in this manner assist reactions where the addition of heat is desirable.

In some cases sulphur dioxide may also be utilized and the sulphur trioxide or sulphuric acid formed may be removed after the reaction zone, the heat of combustion of the sulphur dioxide to the sulphur trioxide in this case also advantageously affecting the catalytic reaction.

In a preferred embodiment of the present in- 15 vention, water vapor in the form of steam may be added to the reaction gases entering a catalytic ammonia oxidation process. The combustion gas mixture leaving a combustion chamber or converter consists usually mainly of nitrogen, oxygen, water vapor and nitric oxide (NO); the object of the whole process is the production of concentrated nitrogen oxides, particularly nitrogen peroxide (NO2) and concentrated nitric acid, by the oxidation of the nitric oxide (NO) and the condensation or absorption of the oxidized gases. Preferably to prevent the formation of diluted nitric acid, this water is removed from the reaction mixture after passage through the reaction zone before the recovery of the nitrogen oxides or nitric acid.

If besides the addition of Water vapor in the form of steam, sulphur dioxide is also added to the reaction gases, sulphuric acid may be conveniently separated from the reaction mixture before the separation of the nitrogen oxides or nitric acid, the process being subject to such control so that the sulphuric acid may be obtained in any desired concentration aqueous, concentrated, or fuming, and in one instance in a concentration of about 60% strength.

In preliminarily separating various constituents of the gaseous reaction products of the present invention, and particularly water vapor therefrom, prior to separation of the primary reaction products, it is not desirable to cool the gases below the condensation or dewpoint temperature of the mixture, since mist, fog and/or fume formation will occur, which renders particularly difcult effective separation of the gases from the condensed constituents, and the condensed constituents from each other. When such a fume, fog or mist is formed, the gas mixture must be further cooled to such a degree that a w cuIty, all without the necessity of excessive cooll :.eixtureY of all the condensable constituents will tire body of the reaction gases.

be deposited from it. Y

A further object of the present invention therefore is to provide a gas separation process in which it is possible to separate preliminarily various constituents from gas reaction mixtures,

Yand-particularly to separate water vapor from gas mixtures in which it may be contained, without obtaining fogs or mists, from which the desired products may only be recovered with difliing, or any undesirable degree of cooling of the en- In carrying out this object, it'is not possible VtoV use rectification and dephlegmation columns Vor refrigerating installations according to standard operating methods, since in the case of these cooling and'condensingmethods it is necessary to Y regulate the discharge temperature of the gas to performed by placing cold surfaces in the stream of theA reactionV gas as it` flows from the catalytic zone,.and in some instances 4after it has flown through a heat recovery apparatus such as a boiler, under such conditions that the surfaces will become coated with and will collect the desired material which is to be condensed. The

' temperature of the cooling 'surf ace should be such,

35 Y be preliminarily separated or co'densed will be that the partial pressure of ,the constituentV to caused to decrease rapidly inthe direction of the cooling surface, with the result that such constituent is condensed, and/or precipitated in solid Y or liquid form uponthe cooling surface.

After the gas mixture has passed in contact with Va suitable area of cooling surface of this character, the constituent Vto be preliminarily separated Ywill be removed substantially completely, or partially to a desired extent, from the reaction mixture containing the principally de- Y Y sired product.

Although in its preferred application, the present invention contemplates the removal of water vapor from gaseous reaction mixtures, such as will result from catalytic oxidation of ammonia, the application of the invention may be convenientlyV illustrated by giving a specific example as to its employment in the separation of moistureV from air. Y

As a specific example, at atmospheric pressure, it is desired to remove of the water vapor from air containing 11.2% by volume thereof and having a'dewpoint or condensation temperature of In achieving this reduction in water vapor and its partial condensation a wide variety of shapes and forms of cool surfaces may be employed for contact with the gas,and by way of example, aluminum pipes of 10 millimeters in diameter and of one meter in length may be employed. These Vpipes are cooled to aldesired temperature with water of about 2 C., which water should preferably flow in contact with suchpipes in countervcurrent direction to the Vflow of gas.

Such a condenser when the condensate flows concurrently with the gaswith a partial pressure drop of 0.2 atmosphere or more, will remove from Y f the gas 8 liters of liquid water per hour per square meterrof cooling surface. The gas mixture flowing out of the condensing apparatus will'have aV temperature of C. and with a. dewpoint or perature.

condensation temperature of V22.5" C.f Under these circumstances a 3@reduction of the mois- Vture will be obtained.V

When the gas or air to be treated contains a higher percentage of water vapor, wider or conical pipes, or other sizes of pipe lengths, or cooling tubes may be employed. With a lower percentage of Water vapor, it is desirable that the cooling walls or surfaces be maintained ata lower tem- The condensate or the cooling water may ow in the same direction as, orV countercurrentrto, the ow of the gas, or it may flow transversely to the same. In some instances the cooling surface may consist in part or whole of the cold condensate itself or ofthe cooling liquid.

This condensation method is particularly advantageous inasmuch as itis possible to utilize much less cooling surface for the same amount of condensate, Vand also because much less heat Vhas to be removed from the gas mixture Vbeing treated, less refrigeration or cooling capacity is Vtile constituents and solvent vapors frorn'waste gases, and it is also broadly applicable to rectification and fractionation processes.

Y The condensation process of the present invention has special application where it is desired to remove a condensible constituentY from gas mixtures without .at the same time causing Vchemical reaction to take placeor to displace the chemical equilibrium of theY gas mixtures by a substantial change in the temperature thereof. There-V action mixture containing nitrogen oxides and water vapor resulting 'from the catalytic oxidation of ammonia is an example of such a mixture. Y

In carrying out the preferred separation as Y above described, it is desirable to remove the con- Y densate from the cooling surface as soon as possible, so as to prevent any possible further reaction between the condensate and the gas mixture, and also to exclude any possibility of reevaporation. This is most conveniently done by deflecting the gas flow-in whole or part as for r example throughl an angle of to 180 degrees; Y

by imparting to the gas a rotating movement; or by utilizing telescoped tubes or piping, which may have conical ends, and are substantially of different diameters, and so arranged that the gas V will flow from the wider pipe into the narrower pipe, whereas the condensate will flow along the wall of the wider pipe and will not enter into the narrower pipe. In another arrangement the condensatre may be caused to flow transversely to the gas flow, the condensing surfaces being provided Y with ribs for conducting away the condensate. The separation of the condensate may also be desirably effected by mechanical means. Y Y

As an example of the specific application of the present invention, a mixture of nitrogen oxides consisting principally of nitric oxide (NO)` and having a temperature of 200 C. resulting from the catalytic oxidation of ammonia, which may have been passed through a heat recovery apparatus or boiler, is passed into a suitable condenser arrangement. Y cooling surface per ton of ammonia burnt per day, 3A of the water vapor may be separated or condensed from the nitric oxide which is present in With only five square meters ofV 'Y the amount of about 9% by volume with substantially very little absorption of the nitric oxide (NO), absorption of the oxidized nitric oxide, or solution of the nitric oxide itself in said condensate, if any.

The resultant gas containing the nitric oxide may then be passed into the nitric acid recovery plant. By preliminarily separating water vapor in this manner considerable economy may be had in such recovery plant. In one case it was possible to reduce the acid proof cooling surface from 1/2 to 2/3. With nitric acid recovery apparatus of the same capacity an acid of much higher concentration may be obtained and, if desired, the alkaline absorption apparatus used may be omitted or reduced in capacity.

In one instance where an apparatus for the oxidation of ammonia and a condensing separator were arranged in series, and directly connected to each other, with only ve square meters of cooling surface per ton of ammonia, one-half of the Water vapor of the reaction gases is removed, even in a case where the reaction mixture contains as much as 30% by volume of oxygen. In carrying out this condensation it was only necessary to reduce the temperature of the gaseous mixture to 70 to 80 C.

I'o contrast this process with an ordinary separation process, Where the gases were cooled below the dewpoint or condensation temperature, at least 3 times as much cooling surface is required. Moreover, a condensate consisting of dilute nitric acid is produced which will not serve either as production acid for commercial sale, nor can it be used as an absorption agent for the oxidized nitrogen oxides, as may the aqueous condensate produced according to the present invention, which aqueous condensate is substantially free of nitrogen oxide.

In working with reaction mixtures rich in oxygen it is possible to effect a substantial increase in the obtainable acid concentration by the method of the present invention, this being particularly true in all instances where Water vapor is formed in the reaction mixture and/or is added to the reaction gases. For example, with a reaction mixture containing ammonia and an air mixture containing 60% by volume of oxygen produced by the fractional distillation of liquid air, as according to our Patent No. 1,850,129, an acid of 40 B. may be obtained with a total yield of about If pure oxygen is used, gaseous or liquid nitrogen tetroxide, or a mixture of nitrogen peroxide and aqueous nitric acid may be prepared, which may be readily processed to form a highly concentrated nitric acid, all without a complicated arrangement of towers, pumps, elevating conduits, ventilators, and other elements now constituting conventional condensation apparatus commonly in use.

To give one specific example, a reaction mixture of 1 volume of ammonia with 1.5 to 2.5 volumes of undiluted 'oxygen is passed through a catalytic oxidation apparatus, as disclosed in our Patent No. 1,850,129. It is possible to separate a greater portion of the Water formed in the reaction mixture, or added to the gas before introduction to the catalytic zone, even though the exit gases have a temperature above C. for example varying from to 190 C. It will be noted in this example the temperature of the effluent gas mixture is above the boiling point of the separated or condensed constituent, a result which can only be obtained from highly concentrated mixtures of nitric oxide and oxygen.

The method of the present invention may also be readily applied to the separation of water, ammonium salts, and hydrocyanic acid from ammoniacal gas mixtures, as are obtained in the hydrocyanic acid synthesis from ammonia and carbon monoxide, and in processes involving the production of cyanamide. By so removing the reaction products from the gas mixtures, the residual unreacted gases may be returned to the reaction for retreatment.

It will be noted according to the present invention that a gas or gaseous mixture containing a vaporized liquid constituent, particularly water, in amount much less than that required for saturation, may be treated to still further reduce the degree of saturation Without decreasing the temperature to the point of saturation, and that this is done in the preferred embodiment of the present invention by passing the partly saturated gases over surfaces which have been cooled to a temperature far below the saturation temperature,or dewpoint, at which normally condensation commences to be effective.

The following examples will more clearly illustrate the exact differences between the present application and processes previously employed:

Ema/mp2@ 1.-A hot mixture of air containing moisture vapor'is passed through a cooling ap-paratus according to the present invention to remove three-quarters` of its moisture or water content. The air mixture, when it passes into the cooling apparatus, has a dew point or saturation temperature of 48 C., and when it leaves the cooling apparatus it has a temperature substantially above its saturation point or dew point, namely about 80 C.

The dew point at this time or saturation temperature is 22.5 C. In the cooling apparatus the partial pressure drop in the gas body as it enters the cooling apparatus is 0.2 atmosphere per centimeter as measured from the gas stream toward the cooling surface and this partial pressure drop will be lowered as the gas flows through the cooling apparatus as more and more of the Water vapor content is removed.

The cooling apparatus includes aluminum tubes about l0 millimeters in diameter and about 1 meter in length and the air current is caused to pass through these tubes. On the outside of the tubes is passed cooling water in counter current to the flow of the gases said cooling water having a temperature of about 2 C.

The condensate is causd to flow on the cooling surface in the same direction as the stream of gas and 8 liters of water per hour are removed as condensate per square meter of cooling surface.

It will be noted that the incoming temperature of 500 C. and the outgoing temperature of 80 C. are always substantially abo-ve the dew point or saturation temperatures, which are respectively 48 C. and 221/2 C.

Eample 2.-An ammonia combustion mixture containing about 9% by Volume of nitric oxide and 14% by volume of water vapor and having a temperature of about- C. is passed into a cooling apparatus under a pressure of 1 atmosphere. The temperature of the leaving gas is regulated to about 42 C. With a cooler having 5 square meters of cooling surface per-ton of ammonia burned per day, about three-quarters of the water formed in the reaction was removed, containing very little nitric acid. This removed Y of theowor" the gases.

Y water might be used for the absorption of the nitrogen oxides in the recovery thereof. The

hot gases in the cooling apparatus pass through tubes of acid-prooi` steel of about 10 millimeters in diameter. y

These tubes are cooled by water of about 10 C. iiowing in counter-current to the direction i The igases leaving the cooling apparatus had a Ysaturation temperature of about 29 C. so that they contain about' half as much water as would correspond to their content at a saturation temperature of 42 C., whichwwas ,theirV temperature at the exit. .'Erample 3 A gas mixture containing 30 to 35% by volume o1" ammonia and the residue Voxygen is passed in contact with a catalyst consisting of platinum or platinum alloys under such conditions as to cause oxidation of the ammonia tonitric oxide. Steam or water may be added to theY gas mixture before itis subjectedto the catalysis. After the catalysis, the reaction gas mixture is contacted withY tubes through which cold water is iowing, said tubes being of Vacidproof steel and being for example of 8 to Y12Y millimeters in diameter. The cooling water may have a temperature of 30 to 8 Cfand the amount of it may be so regulated that the' temperature riseof the cooling water will be about 30 C. in passing through theV apparatus. The gases, after catalysis, and before theyrare cooled, may haveV a temperature of 209` C. and after leaving the cooling apparatus they may have a temperature of 140 C. With a gas outlet temperatureY of 140 C. and :a saturation or condensation tempera- -ture oi 70 C., these outlet gases from the cooling apparatus will contain one-tenth as much moisture as will correspond to their saturation ternperature at 140 C.

The accompanying drawings illustrate'in diagrammaticffashion the processes of the present recovery boiler 3 a preheater for the atmospheric Y air mixed with the ammonia may be employed.

l The gas mixture leaving the boiler 3 consists of the products of combustion of ammonia and. contains'about 9% by volume of nitric oxide.

This mixture flows into a metal cooler 4 which contains a plurality of tubes which are connected in series. The tubes' which are cooled from the outsidebyV cold water,V are made of acid-proof steel and have an internal diameter of about 10 mm. The purpose of 'the'cooler is to cause the separation of water as a condensate.

The element i the boiler 3 and the cooler 4 are Vpreerably arranged in series and directly connected to each other, Yas shown. In the apparatus shown the working pressure may be l atmosphere. The normal cooling water used enters the cooler at laat a temperature of 10 C. and may leave the cooler at 4b. The gases entering the cooler 4 mayY have aternperature of 160 C. The tem-V perature of the gas mixture which leaves the cooler may be maintained at 472 C. Under these circumstances with only ve square meters of cooling surface per ton of oxidized ammonia '3A of the water resulting from the reaction may be condensed.A

This condensed Vwater contains so little nitric acid that it may be directly fed to the device in lwhich the nitrogen oxides are finally absorbed. As shown, the aqueous condensate is drawn oi at 4c and forced by the pump 5 through the tube Y5 I3 to the absorption towers 9 and I 0 in which the nal absorption takes place.V

The eiiluent nitric oxide from the cooler vthen flows through the cooling and oxidizingtower 8 to the absorption towers 9 and I0. The ilow of 10 the gases is caused or assisted by a blower 6 which is driven by a motor 'I. The cooling Vwater enters the vessel 8 at 8a, flows vthrough the cooling tubes 8b and leaves the vessel at 8c. V

The absorption plant is shown as equipped 15 with two absorption towers 9 and I0 Vin which plates are arranged in superimposed relationship. Each plate carries a layer of liquid through which the ascendinggas current passes in iinely divided state. The towers '9 and I0 may be 20 cooled from the outside by cooling coils'(not shown) which are arranged above the said plates and through which the cooling-,Water is flowing. The liquid flows downward from one sieve plate to the next. 275V Y The gas mixture leaving the cooling tower 8 enters the bottom of the tower 9 andV flows upwardly therethrough. From the top of the tower 9 the gas mixture is conducted to the bottom of the tower I0 and also flows upwardly there- 3,0 through. The condensate formed in the cooler 8 is supplied Yto an absorption plate in the absorp- .tion tower the concentration of the acid on which is about the same as the acid concentration of the condensate. For example it may be supplied 35 either to the top of the tower 9 or to the plate at the level indicated 'at I2 (which may be at any Vdesired height in the tower 9).

The aqueous condensate separated in the cooler 4 is introduced into the upper end of the tower I0. 40

If required, additional water may be supplied at I4. The liquid iiows from the top of the tower Il) to the Vbottom of the same, counter currentV to the flow of the nitrogen oxide mixture and-is thereby continuously enriched with nitric acid. 4.5 From the bottom of the tower II! thefluid is forced. into the top of the tower 9 by a pump I5.V The concentrated acid obtained may be drawn off at I6. The end gases escape from the tower I0 at I'I.

'I'he mixture obtained by the combustion of-:50V ammonia, as stated above, contains about.9% by volume of NO. The mixture also contains about 14% by volume ofsteam, or Vwater vapor, and oxygen Vand nitrogen.

Since @ya of the water formed in thereaction is condensed in the coolerY 4 about 4.1% by volurneof Water vapor will remain in the gas mixture. The gas mixture leaving the cooler 4 will have a dew point or saturation of about 29 C., but the actual temperature of the gases will be about 42 C..V 60 At apressure of l atmosphere this last-mentioned temperature would correspond to a water.r vapor content of Vthe gas of 8.4% by volume.

The gas mixture leaving the cooler 4 therefore only contains half of the amount of water vapor which it would contain if its exit temperature were its saturation temperature. V Y

The oxidation of NO to NO2 takes place inthe cooling tower '8.

In Figure 2 a mixture consisting of l part by 7,0V volume of NH3 and 1 to 4 parts by volume of oxygen (which may be produced in any desiredV manner, as for example by electrolysis, by liquefying of air or the like) are passed'at 3| into an ammoniacombustion chamber 32. The gasv mixture passes through a perforated plate 32a which is covered by a layer of water as disclosed in U. S. Patent 1,850,129 and thenthrough a platinumrhodium catalyst at 32h. The combustion mixture flows through the conduit 33 into the steam boiler 34. The steam produced ows through the pipe 35 back into the ammonia combustion chamber 32 in which the steam is mixed with the gas mixture entering at 3 I From the boiler 34 the gas mixture flows into a cooler 36 consisting of rolled in tubes of acidproof steel which may have an internal diameter of about 8 or 10 mm. The tubes are connected in parallel and are cooled by water flowing around them. In the cooler the condensate is separated from the gases. The cooling water enters at 36a and leaves at 36h. The aqueous condensate contains in large part the water which was supplied through the conduit 35 as vapor, and by vaporization from the layer of liquid on the perforated plate 32a as well as that produced by the co-mbustion of ammonia. This aqueous condensate is drawn off at 36e.

The cooling water employed enters the cooler 36 at a temperature between 0 and 30 C., as for example 20 C. 'Ihe gas mixture may ilow from the boiler 34 into the cooler 36 at atmospheric pressure and at a temperature of about 200 C.

It is desirable that the temperature of the gas, when it leaves the cooler, be higher than C. Usually the temperature is between 100 and 200 C. and may be about C. The gas mixture which leaves the bottom of the cooler 36 after separation of the aqueous condensate has a temperature which is higher than 100 C. and a dew point or saturation temperature which is considerably below 100 C., as for example between 50 and '70 C.

This gas mixture contains less than the half of the amount of water which it would contain if it were saturated at the outlet temperature of 140 C. and if it has a dew point of about 70 C. it contains less than T15 of the amount of water it would contain if its dew point were 140 C. A condensate poor in nitrogen oxides is obtained from highly concentrated oxygen-containing nitric oxide mixture when the just-described method is employed.

The steam produced in the boiler 34 may be added in part or in whole to the fresh' gas. The process may of course also be employed in connectionwith ammoniacombustion mixtures which have been prepared catalytically without addition of steam as for example by cooling of the catalyst.

The gas mixture leaving the cooler 36 may be passed through a pipe 31 and a cooler 38 and into a liqueer 39, in which at say about 10 C., liquid nitrogen tetroxide is produced by condensation.

In the cooler 38,l there are tubes externally cooled by water which is introduced at 38a and drawn off at 38h. The gas mixtures pass through the tubes 38o.

The aqueous nitric acid is drawn oi from the cooler 33 at 40 together with the condensed liquid nitrogen tetroxide from the liqueer 39.

The gas which is not liqueed in 39 ows through a tube 4I and an absorbing tower 42 and escapes at 43.

The nitrogen oxides which are still present in this gas are absorbed by highly concentrated nitric acid, which enters at the top of the tower 42 and flows down through the tower counter current to the flow of the gases. This concentrated nitric acid, after enrichment with the residual nitrogen oxides is forced through a tube 45 to a tower 46 by the pump 44.

The upper part of the tower 46 is equipped with a cooling water jacket 41 and the lower part 5 is equipped with a steam jacket 48. Cooling water is supplied at 41a and escapes at 41h. Steam is supplied at 48a and the condensate formed escapes at 48D.

The dissolved nitrogen oxides are evolved in 10 the lower part of the tower 46 and any nitric acid carried thereby is condensed in the upper part of the tower. These nitrogen oxides are thereupon introduced into the cooler 38 by the tube 49, which may be connected to the conduit 31. 15

The highly concentrated nitric acid, from which the nitrogen oxides have been removed in the tower 46, flows from the bottom of the tower into a jacketed cooler 56 and is thereupon pumped to the tower 42 through the tube 52 and the 20 jacketed cooler 33 by the pump 5i.

Cold brine, (for example having a temperature of 12 C.) enters the cooler 53 at 53a, leaves the same at 53h, enters the brine jacket of the tower 42 at 42a, leaves the same at 42h, flows into the 25 liqueiier 39 at 39a, leaves the same at 39h, (for example at a temperature of 9 C.)

The oxidation of NO tc NO2 takes place in tl cooler 38.

The mixture of aqueous nitric acid and nitro- 30 gen tetroxide at 40 may be used to produce highly concentrated nitric acid.

What is claimed is l. A process of carrying out gas reactions which comprises reacting together a plurality of gases which will form a condensible constituent and a desired gaseous reaction product, preliminarily condensing a major part of said condensible constituent from the gases while maintaining said gases above the saturation temperature or dew 40 point for said constituent and then subsequently recovering the reaction product, said condensing being effected by contacting the gases with cold surfaces which are maintained at a temperature substantially below the dew point or saturation temperature for the condensible constituent, whereby said condensible constituent will be condensed in large part upon said cold surfaces and may be removed from said cold surfaces, the cooling of said gases being so regulated as to avoid cooling said gases down to the dew point or saturation temperature for said condensible constituent.

2. A process of carrying out gas reactions which 55 comprises reacting together a plurality vof gases which will form water vapor and a desired gaseous reaction product, and preliminarily condensing a major part of the water vapor while maintaining the gases at a temperature substan- 60 tially above the saturation point or dew point for the water vapor, said condensing being effected by contacting the gases with cold surfaces which are maintained at a temperature substantially below the dew point or saturation temperature 65 for the condensible constituent, whereby said condensible constituent will be condensed in large part upon said cold surfaces and may be removed from said cold surfaces, the cooling of said gases being so regulated as to avoid cooling said gases 70 down to the dew point or saturation temperatureV for said condensible constituent.

3. A process of carrying out gas reactions which comprises reacting together a plurality of gases which will form a condensible constitu-*75 ing said mixture through a catalytic zone forming a gaseous mixture of nitric oxide7 Water vapor and oxygen, treating the gases to condense a large proportion of the Water vapor present Without any substantial oxidation of the nitric oxide Iand Without any substantial solution and absorption of the nitric oxide in the water, then oxidizing the nitric oxide to form nitrogen peroxide, and further treating said nitrogen peroxide to form concentrated nitric acid. 

